Reader with decoupled magnetic seed layer

ABSTRACT

An apparatus comprising a base shield and a sensor stack, wherein the base shield is separated from the sensor stack via a first soft magnetic layer that is magnetically decoupled form the base shield.

PRIORITY CLAIM

This application is a divisional of U.S. application Ser. No. 13/791,334filed Mar. 8, 2013, the entire disclosure of which is incorporatedherein by reference.

BACKGROUND

In a magnetic data storage and retrieval system, a magnetic read/writehead includes a reader portion having a magnetoresistive (MR) sensor forretrieving magnetically encoded information stored on a magnetic disc.Magnetic flux from the surface of the disc causes rotation of themagnetization vector of a sensing layer of the MR sensor, which in turncauses a change in electrical resistivity of the MR sensor. The changein resistivity of the MR sensor can be detected by passing a currentthrough the MR sensor and measuring a voltage across the MR sensor.External circuitry then converts the voltage information into anappropriate format and manipulates that information to recover theinformation encoded on the disc.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Otherfeatures, details, utilities, and advantages of the claimed subjectmatter will be apparent from the following more particular writtenDetailed Description of various implementations and implementations asfurther illustrated in the accompanying drawings and defined in theappended claims.

Implementations described and claimed herein provide an apparatuscomprising a base shield and a sensor stack, wherein the base shield isseparated from the sensor stack via a first soft magnetic layer that ismagnetically decoupled from the base shield. These and various otherfeatures and advantages will be apparent from a reading of the followingdetailed description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The described technology is best understood from the following DetailedDescription describing various implementations read in connection withthe accompanying drawings.

FIG. 1 illustrates a perspective view of an example recording deviceusing a reader disclosed herein.

FIG. 2 illustrates a schematic block diagram of an exampleimplementation of the reader disclosed herein.

FIG. 3 illustrates another schematic block diagram of an exampleimplementation of the reader disclosed herein.

FIG. 4 illustrates another schematic block diagram of an exampleimplementation of the reader disclosed herein.

FIG. 5 illustrates another schematic block diagram of an exampleimplementation of the reader disclosed herein.

FIG. 6 illustrates a graph of a transition readback signal obtained byan example reader disclosed herein.

FIG. 7 illustrates a graph of the PW50 gain as a measure of thickness ofthe soft decoupled magnetic layer for an example reader disclosedherein.

DETAILED DESCRIPTIONS

There is an increasing demand for high data densities and sensitivesensors to read data from a magnetic media. Giant Magnetoresistive (GMR)sensors that have increased sensitivity consist of two soft magneticlayers separated by a thin conductive, non-magnetic spacer layer such ascopper. Tunnel Magnetoresistive (TMR) sensors provide an extension toGMR in which the electrons travel with their spins orientedperpendicularly to the layers across a thin insulating tunnel barrier.An antiferromagnetic (AFM) material (called the “pinning layer (PL)”) isplaced adjacent to the first soft magnetic layer to prevent it fromrotating. AFM materials exhibiting this property are termed “pinningmaterials”. With its rotation inhibited, the first soft layer is termedthe “pinned layer”. The second soft layer rotates freely in response toan external field and is called the “free layer (FL).”

To operate the MR sensor properly, the sensor should be stabilizedagainst the formation of edge domains because domain wall motion resultsin electrical noise that makes data recovery difficult. A common way toachieve stabilization is with a permanent magnet abutted junctiondesign. In this scheme, permanent magnets with high coercive field(i.e., hard magnets) are placed at each end of the sensor. The fieldfrom the permanent magnets stabilizes the sensor and prevents edgedomain formation, as well as provides proper bias. In order to increasethe stiffness of the PL, “synthetic antiferromagnet” (SAF) is used inthe PL. The use of the AFM/PL allows for consistent and predictableorientation of the SAF structure. Furthermore, the use of AFM/PL alsoprovides a stable structure to enable high amplitude linear response fora reader using the MR sensor.

The assembly of the various layers the GMR/TMR sensors, as discussedabove, is also referred to as a sensor stack. Such sensor stack may besurrounded by a base shield and a top shield to shield the sensor fromany magnetic influences that are generated from other components of thetransducer head. In such an implementation, the distance between the topshield and the base shield is referred to as the shield-to-shieldspacing (SSS). The pulse width fluctuations PW50 of magnetic sensors,which determine the signal-to-noise (SNR) ratio in a recording systemdepends on the SSS of the head. Specifically, a reduction in the SSSleads to reduction in the value of the PW50 and therefore, an increasein the value of the SNR for the recording system. However, using SSSreduction to achieve lower PW50 has its limits.

An example reader sensor assembly disclosed herein provides alternativemethods for reducing the PW50 of a reader sensor without reducing theSSS of the reader sensor. Specifically, the reader sensor assemblyincludes a reader stack surrounded by base shield and a top shieldwherein at least one of the base shield and the top shield is separatedfrom the sensor stack by a soft magnetic seed layer that is decoupledfrom the base shield or the top shield, respectively. In an alternativeimplementation of such reader sensor, only a portion of the softmagnetic seed layer is decoupled from the base shield or the top shield.Providing such partial decoupled seed layer allows to maintain thestability of the sensor while at the same time decreasing the PW50 ofthe sensor stack to improve the SNR of the recording system.

FIG. 1 illustrates a perspective view of an example recording device 100using a reader disclosed herein. The recording device 100 includes adisc 102, which rotates about a spindle center or a disc axis ofrotation 104 during operation. The disc 102 includes an inner diameter106 and an outer diameter 108 between which are a number of concentricdata tracks 110, illustrated by circular dashed lines. The data tracks110 are substantially circular and are made up of regularly spacedpatterned bits 112, indicated as dots or ovals on the disc 102 as wellas in an exploded view 140. It should be understood, however, that thedescribed technology may be employed with other types of storage media,including continuous magnetic media, discrete track (DT) media, etc.

Information may be written to and read from the bits 112 on the disc 102in different data tracks 110. A transducer head 124 is mounted on anactuator assembly 120 at an end distal to an actuator axis of rotation122 and the transducer head 124 flies in close proximity above thesurface of the disc 102 during disc operation. The actuator assembly 120rotates during a seek operation about the actuator axis of rotation 122positioned adjacent to the disc 102. The seek operation positions thetransducer head 124 over a target data track of the data tracks 110.

The exploded view 140 illustrates data tracks 142 and an expanded viewof a transducer head 144 having a writer 148 and a reader sensor 150.Furthermore, an example implementation of the reader sensor 150 isillustrated by a block diagram 160. Specifically, the block diagram 160illustrates an air-bearing surface (ABS) view of the reader sensor 150.In the illustrated implementation, the reader sensor 150 is illustratedto include a base shield 162 and a top shield 164, with a sensor stack166 formed between the base shield 162 and the top shield 164.

Furthermore, the sensor stack 166 is separated from the base shield 162by a base seed layer 168 that is at least partially decoupled from thebase shield 162. In the illustrated implementation, a center portion 170of the base seed layer 168 is not decoupled from the base shield 162,whereas the outer portion 172 of the base seed layer 168 is decoupledfrom the base shield 162. Furthermore, the sensor stack 166 is separatedfrom the top shield 164 by a top seed layer 174 that is at leastpartially decoupled from the top shield 164. In the illustratedimplementation, a center portion 176 of the top seed layer 174 is notdecoupled from the top shield 164, whereas the outer portion 178 of thetop seed layer 174 is decoupled from the top shield 164. The base seedlayer 168 and the top seed layer 174 may be made of soft magnetic seedlayer material and providing one or both of the base seed layer 168 andthe top seed layer 174 results in decreased PW50 for the sensor 150. Onthe other hand, providing the partial coupled magnetic layers in theouter portions of the one or both of the base seed layer 168 and the topseed layer 174 results in increased stability of the sensor 150.

FIG. 2 illustrates a schematic block diagram of an ABS view of anexample implementation of the reader 200 disclosed herein. The reader200 includes a base shield 210 and a top shield 212 around a sensorstack 214. The base shield 210 and the top shield 212 may be made of maybe made of a magnetic material, such as NiFe, NiFeCu, NiCoFe, etc. Inone implementation, the reader 200 includes a decoupled base seed layer216 on the surface of the base shield 210. Thus, the base shield 210 isseparated from the sensor stack 214 by the decoupled base seed layer216. Specifically, the decoupled base seed layer 216 is magneticallydecoupled from the base shield layer 210. In one implementation, thedecoupled base seed layer 216 is made of soft magnetic material such asNiFe, NiFeCu, NiCoFe, etc and is separated from the base shield 210 by athin layer of non-magnetic material 218 that is between the decoupledbase seed layer 216 and the base shield 210. For example, such thinlayer of non-magnetic material 218 may be created using a dusting of thenon-magnetic material on the base shield 210 or on the decoupled baseseed layer 216. Examples of such non-magnetic material include Tantalum,Tantalum compounds, etc.

The decoupled base seed layer 216 improves the PW50 of the reader 200because the effective in-plane exchange coupling between the base shield210 and the decoupled base seed layer 216 is very low or substantiallyequal to zero. Thus, the closeness of the surfaces in the decoupled baseseed layer 216 results in higher ratio of the Zeeman energy to theexchange energy, wherein the Zeeman energy is the energy between thebase seed layer 216 and the media from which the data is read. Thehigher Zeeman energy/exchange energy ratio results in easier change inthe local magnetization direction as the sensor moves over the media,thus improving the PW50 of the sensor 200. The improved PW50 increasesthe capability of the sensor 200 to read data with higher lineardensity, thus allowing a recording device using the sensor 200 toprovide higher linear data density and thus more cost effective datastorage capabilities.

The thickness of the seed layer 216 may be 5-15 nm. The thickness of thedecoupled base seed layer 216 determines the exchange of magnetic energybetween the base shield 210 and the decoupled base seed layer 216.Specifically, if the decoupled base seed layer 216 is too thin, it wouldnot be able to accommodate the magnetic flux from the media. On theother hand, if the decoupled base seed layer 216 is too thick, itreduces the PW50 gain.

FIG. 3 illustrates another schematic block diagram of an ABS view of anexample implementation of the reader 300 disclosed herein. The reader300 includes a base shield 310 and a top shield 312 around a sensorstack 314. The base shield 310 and the top shield 312 may be made of maybe made of a magnetic material, such as NiFe, NiFeCu, NiCoFe, etc.Furthermore, the reader 300 also includes a decoupled base seed layer316 on the surface of the base shield 310 and a decoupled top seed layer318 on the surface of the top shield 312. Specifically, the decoupledbase seed layer 316 is magnetically decoupled from the base shield 310and the decoupled top seed layer 318 is magnetically decoupled from thetop shield 312. In one implementation, each of the decoupled base seedlayer 316 and the decoupled top seed layer 318 is made of soft magneticmaterial such as NiFe, NiFeCu, NiCoFe, etc. The forming of the decoupledseed layers 316 and 318 increases the ratio of the Zeeman energy toexchange energy on both sides of the sensor 314, resulting in improvedPW50 for the reader 300.

FIG. 4 illustrates another schematic block diagram of an ABS view of anexample implementation of the reader 400 disclosed herein. The reader400 includes a base shield 410 and a top shield 412 around a sensorstack 414. The base shield 410 and the top shield 412 may be made of amagnetic material, such as NiFe, NiFeCu, NiCoFe, etc. Furthermore, thereader 400 also includes a decoupled top seed layer 418 on the surfaceof the top shield 412. Specifically, the decoupled top seed layer 418 ismagnetically decoupled from the top shield 412. In one implementation,the decoupled top seed layer 418 is made of soft magnetic material suchas NiFe, NiFeCu, NiCoFe, etc. The forming of the decoupled top seedlayer 418 increases the ratio of the Zeeman energy to exchange energy ontop shield side of the sensor 414, resulting in improved PW50 for thereader 400.

FIG. 5 illustrates another schematic block diagram of a side view (notto scale) of an example implementation of a reader 500 disclosed herein.The reader 500 includes a sensor stack 512 with each of a base shield514 and a top shield 516 on each sides of the sensor stack 512. Notethat for the clarity of illustration, the distance between the baseshield 514 and the sensor stack 512 is illustrated to be different thanthe distance between the top shield 516 and the sensor stack 512. Thereader 500 may be part of a transducer head moving on an ABS 520. Thebase shield 514 includes a base seed layer 522 that is formed on thesurface facing the sensor stack 512. Similarly, the top shield 516 alsoincludes a top seed layer 524 that is formed on the surface facing thesensor stack 512.

Each of the base seed layer 522 and the top seed layer 524 includes acenter portion that is decoupled from the base shield 514 and the topshield 516, respectively. Specifically, the base seed layer 522 includesa decoupled base seed layer 526 that is magnetically decoupled from thebase shield 514. The remaining base seed layer 522 is magneticallycoupled with the base shield 514. Similarly, the top seed layer 524includes a decoupled top seed layer 528 that is magnetically decoupledfrom the top shield 516. The remaining top seed layer 524 ismagnetically coupled with the top shield 516. Note that in theimplementation illustrated in FIG. 5, the base center portions 526 and528 are illustrated to have a square shape, in an alternativeimplementation, these center portions may also have other shapes, suchas rectangular, circular, oval, etc.

In one implementation, the distances between the edges of the sensorstack 512 and the edges of the decoupled center portions 526 and 528 areat least twice the SSS. As an example, for the top seed layer 524, thedistance 530 between an edge of the sensor stack 512 and an edge of thetop center portion 528 must be at least twice the SSS 532 (note that thedistances as seen in the figures are not to scale). In other words, thetotal width 534 (and length) of the top center portion 528 is greaterthan the 4*SSS 532. Similar dimensions also apply to the base centerportion 526 of the bottom seed layer 522. Such dimensions of the coupledbase seed layer 522 and the top seed layer 524 ensure that the stabilityof the reader 500 is not adversely affected in view of the introductionof the base center portion 526 that is decoupled to the base shield 514and the top center portion 528 that is decoupled from the top shield516.

Because the reader 500 includes the decoupled portions in the base seedlayer 522 and the top seed layer 524 in the vicinity of the sensor stack512, the reader 500 exhibits lower PW50 and therefore higher lineardensity capabilities. However, because only a small portion of each ofthe base seed layer 522 and the top seed layer 524 is decoupled from thebase shield 514 and the top shield 516 respectively, the reader 500 alsoprovides higher stability compared to a reader where the entire baseseed layer and top seed layer were decoupled from a base shield and atop shield, respectively.

FIG. 6 illustrates a graph 600 of improvement in the transition readbacksignal obtained by an example reader disclosed herein. Specifically, thegraph 600 illustrates a line 610 that represents the readback derivativewithout any decoupled seed layer on either of the base shield and thetop shield and a line 612 that represents the readback derivative with adecoupled seed layer on the base shield. As illustrated the PW50, asillustrated by the line 620 is higher for the readback derivative 610compared to the readback derivative 612. Specifically, in theillustrated example, the PW50 improved from 28.2 nm to 27.1 nm,resulting in increased linear density capabilities for the reader.

FIG. 7 illustrates a graph 700 of modeled gain in PW50 as a function ofmagnetic layer thickness for an example reader disclosed herein.Specifically, graph 700 includes a line 710 illustrating the PW50 of asensor without any decoupled seed layer between a sensor stack and abase shield layer. The line 712 illustrates the PW50 as a function ofthe thickness of a decoupled seed layer formed on the base shield. Thedifference between the line 710 and 712 is the decrease in the PW50 ofthe sensor resulting from the introduction of the decoupled seed layerbetween the base shield and the sensor stack. For example, for 10 nmthickness of the decoupled seed layer, the PW50 improves byapproximately 1.1 nm (28.2 nm-27.1 nm). This improvement has also beenobserved experimentally. As the thickness of the decoupled seed layerincreases, the decrease in the PW50 decreases. The decreased PW50improves linear density capabilities of the reader.

The above specification, examples, and data provide a completedescription of the structure and use of example implementations of theinvention. Since many implementations of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended. Furthermore,structural features of the different implementations may be combined inyet another implementation without departing from the recited claims.The implementations described above and other implementations are withinthe scope of the following claims.

What is claimed is:
 1. An apparatus comprising: a base shield; a sensor stack; and a base seed layer separating the base shield from the sensor stack, wherein the base seed layer comprises: a base coupled seed section that is coupled with the base shield; and a base uncoupled seed section that is uncoupled with the base shield, wherein the base uncoupled seed section covers a base window surrounding the sensor stack.
 2. The apparatus of claim 1, wherein the dimension of the base window beyond the sensor in a direction perpendicular to the direction of the sensor stack is at least twice the dimension of the spacing between the base shield and the top shield.
 3. The apparatus of claim 2, wherein the base uncoupled seed section is uncoupled from the base shield using a layer of non-magnetic material.
 4. The apparatus of claim 1 further comprising a top shield located on a side of the sensor stack opposite the base shield, the top shield separated from the sensor stack with a top seed layer.
 5. The apparatus of claim 4, wherein the top seed layer comprises: a top coupled seed section that is coupled with the top shield; and a top uncoupled seed section that is uncoupled with the top shield, wherein the top uncoupled seed section covers a top window surrounding the sensor stack.
 6. The apparatus of claim 5, wherein the top uncoupled seed section is uncoupled from the top shield using a layer of non-magnetic material.
 7. The apparatus of claim 5, wherein the dimension of the top window beyond the sensor in a direction perpendicular to the direction of the sensor stack is at least twice the dimension of the spacing between the base shield and the top shield.
 8. The apparatus of claim 7, wherein the base coupled seed section and the top coupled seed section are made of at least one of NiFe, NiFeCu, and NiCoFe.
 9. The reader sensor of claim 6, wherein the sensor stack is located on a read head of a disc drive.
 10. A reader sensor comprising: a sensor stack; a top shield and a base shield; a base seed layer separating the sensor stack from the base shield, wherein the base seed layer is at least partially uncoupled with the base shield; a top seed layer separating the sensor stack from the top shield, wherein the top seed layer is at least partially uncoupled with the top shield.
 11. The reader sensor of claim 10 wherein a dimension of a section of the base seed layer, which is uncoupled with the base shield, in a direction perpendicular to the direction of the sensor stack is at least twice the dimension of the spacing between the base shield and the top shield.
 12. The reader sensor of claim 10 wherein a dimension of a section of the top seed layer, which is uncoupled with the top shield, in a direction perpendicular to the direction of the sensor stack is extends beyond the sensor stack by at least twice the dimension of the spacing between the base shield and the top shield.
 13. A reader sensor comprising: a sensor stack; a top shield and a base shield; a base seed layer separating the sensor stack from the base shield, wherein the base seed layer is at least partially uncoupled with the base shield, wherein dimension of a section of the base seed layer, which is uncoupled with the base shield, in a direction perpendicular to the direction of the sensor stack is at least twice the dimension of the spacing between the base shield and the top shield. 